The goal of this proposal is to examine the functions of the Nova family of paraneoplastic neurologic disease antigens in neurons, and to compare them with those of the closely related fragile X mental retardation protein FMRP. We have developed new methodology to identify neuronal RNAs bound by these proteins. Specific hypotheses regarding these interactions will be examined in vitro, and extended in vivo, using genetically modified mice, to provide direct evidence for the function of these RNA binding proteins in the brain. We will identify new RNA targets using RNA selection from a transcribed sequence library, by biochemical purification, and by using array analysis. We will explore two hypotheses regarding how Nova functions on these RNAs. First, we will examine the role of Nova in binding nuclear RNA sequences for the regulation of alternative splicing. Second, we will explore the function of cytoplasmic Nova, following up preliminary data suggesting that it is involved in translational control. We will compare our findings with actions of FMRP on target RNAs we have identified. To validate these studies, we will move from in vitro and cell based biochemistry to in vivo biochemistry by repeating our analyses of Nova and FMRP function in genetically defined mice. One set of mice will include Nova and FMRP KO mice. A second set will consist of BAC transgenic mice modified to test the function of specific protein-RNA actions we have identified. These studies will allow us to formulate a model comparing and contrasting the role that the Nova and FMRP RNA binding proteins in neurons and in neurologic disease.